The present invention relates to a long fiber-reinforced polypropylene resin composition which is suited for producing not only small-sized molded articles but also wide-ranged molded articles from medium-sized ones to large-sized ones and to a molded article obtained from the same. Specifically, it relates to a molded article which is excellent in a mechanical strength obtained particularly when it is molded into a medium-sized to large-sized molded article, particularly a mechanical strength in a direction perpendicular to a flow direction of the resin, and therefore has a small anisotropy in a mechanical strength and which is excellent as well in an impact strength and to a long fiber-reinforced polypropylene resin composition which provides the same.
A so-called long fiber-reinforced polypropylene resin composition obtained by impregnating a reinforcing continuous fiber bundle with a molten polypropylene resin and then pultruding it to pelletize to a length of 2 to 50 mm provides a molded article which is excellent in a mechanical strength, an impact resistance and a heat resistance and therefore is widely used for uses in car parts, industrial parts and the like.
However, when molding a long fiber-reinforced polypropylene resin composition into medium-sized to large-sized molded articles, the mechanical strength and the impact resistance are still unsatisfactory, and particularly the mechanical strength in a direction perpendicular to a flow direction of the resin is short. Accordingly, the molded articles have a large anisotropy in a strength, and it is the existing state that the uses thereof are restricted.
A composition obtained by impregnating a reinforced fiber bundle with a modified polyolefin blended with an alkaline earth metal compound and then pelletizing it was filed in International Publication WO99/20446 by the present applicants as a long fiber-reinforced polyolefin resin composition providing a molded article which was improved in a mechanical strength. When this composition is molded into small-sized molded articles, the molded articles are improved in a mechanical strength and an impact resistance as compared with those of articles molded from conventional long fiber-reinforced polyolefin resin compositions.
Proposed as a glass fiber-reinforced polyolefin resin composition which is improved in a dispersibility of glass fibers in production and which is less liable to cause breaking of the glass fibers in molding is a glass fiber-reinforced polyolefin resin composition obtained by mixing 10 to 70 parts by weight of pellets which are prepared by blending 100 parts by weight of a mixture comprising 20 to 60% by weight of (Axe2x80x2) a propylene homopolymer and 80 to 40% by weight of glass fibers with 1 to 10 parts by weight of an acid-modified polyolefin having an acid-added amount of 0.1 to 10% by weight and in which a pellet length is 2 to 20 mm and the above glass fiber has substantially the same length as the pellet length with (B) 90 to 30 parts by weight of a propylene-ethylene block copolymer so that the whole amount becomes 100 parts by weight (Japanese Patent Application Laid-Open No. 239286/1993, Japanese Patent Application Laid-Open No. 173329/1995 and Japanese Patent Application Laid-Open No. 237512/1995). When these compositions are molded into small-sized molded articles, the molded articles are improved in a mechanical strength, a durability and an impact resistance as compared with those of articles molded from conventional long fiber-reinforced polyolefin resin compositions.
However, not yet known is a long fiber-reinforced polypropylene resin composition providing a molded article which is excellent in a mechanical strength and an impact resistance even when it is molded into medium-sized to large-sized molded articles and which is improved particularly in a mechanical strength in a direction perpendicular to a flow direction of the resin and therefore has a small anisotropy in a strength. Thus, such composition has been demanded.
An object of the present invention is to provide a long fiber-reinforced polypropylene resin composition which can solve entirely the inconveniences described above, that is, an anisotropy in a mechanical strength, an impact resistance and a strength even when it is molded into medium-sized to large-sized molded articles and which can suitably be used as well for uses in medium-sized to large-sized molded articles. Another object is to provide a molded article obtained from the same.
Intensive investigations repeated by the present inventors in order to obtain a long fiber-reinforced polypropylene resin composition which can solve entirely the inconveniences described above have resulted in finding that very useful for solving the problems described above is a composition obtained by blending a long fiber-reinforced pellet comprising as a base, a specific modified propylene homopolymer compounded with an alkaline earth metal compound with a specific propylene base block copolymer resin as a diluent, and thus they have completed the present invention.
That is, the present invention comprises structures shown below.
(1) A long fiber-reinforced polypropylene resin composition comprising 40 to 85% by weight of (A) a long fiber-reinforced propylene homopolymer pellet shown below and 15 to 60% by weight of (B) a propylene base block copolymer resin having a melt flow rate (230xc2x0 C., 21.18 N; hereinafter abbreviated as MFR) of 50 g/10 min or less:
(A): a long fiber-reinforced propylene homopolymer pellet comprising,
(A1): 20 to 64.9% by weight of a modified propylene homopolymer obtained by modifying a propylene homopolymer with unsaturated carboxylic acid or an anhydride thereof or a mixture of the above modified propylene homopolymer and an unmodified propylene homopolymer, wherein the MFR is 60 g/10 min or more,
(A2): 0.1 to 5% by weight of at least one selected from the group consisting of simple substances, hydroxides and oxides of alkaline earth metals, and
(A3): 35 to 75% by weight of glass long fibers having a length of 2 to 50 mm.
(2) The long fiber-reinforced polypropylene resin composition as described in the above item (1), wherein (A1) the modified propylene homopolymer obtained by modifying the propylene homopolymer with the unsaturated carboxylic acid or the anhydride thereof or the mixture of the above modified propylene homopolymer and the unmodified propylene homopolymer has an MFR of 100 g/10 min or more, and (B) the propylene base block copolymer resin has an MFR of 35 g/10 min or less.
(3) The long fiber-reinforced polypropylene resin composition as described in the above item (1) or (2), wherein (B) the propylene base block copolymer is a high rigid propylene-ethylene block copolymer resin comprising a propylene homopolymer part having an isotactic pentad rate of 0.96 or more and an Mw/Mn (Q value) of 6 or less, and a propylene-ethylene copolymer part.
(4) The long fiber-reinforced polypropylene resin composition as described in any of the above items (1) to (3), wherein
(B) the propylene base block copolymer resin contains 0.0001 to 1% by weight of a nucleating agent based on the propylene base block copolymer resin.
(5) A molded article obtained by molding the long fiber-reinforced polypropylene resin composition as described in any of the above items (1) to (4).
(6) The molded article as described in the above item (5), wherein the glass long fibers contained in the molded article originating in the long fiber-reinforced propylene homopolymer pellet have a residual average fiber length of 1 mm or more.
Any of publicly known processes can be employed as a production process for the propylene homopolymer of (A1) described above constituting (A) the long fiber-reinforced polypropylene homopolymer pellet of the present invention, which is modified with unsaturated carboxylic acid or an anhydride thereof, a so-called modified propylene homopolymer. The modified propylene homopolymer can be obtained, for example, by a process in which a propylene homopolymer is molten and kneaded together with 0.1 to 5 parts by weight of unsaturated carboxylic acid or an anhydride thereof and 0.01 to 0.5 part by weight of an organic peroxide per 100 parts by weight of the above polymer. In the present invention, however, the modified propylene homopolymer has preferably an MFR of 60 g/min or more, more preferably 100 g/min or more and further more preferably 100 to 1,000 g/min from a viewpoint of an effect for improving a mechanical strength and an impact resistance.
Included in (A1) of the present invention is a mixture of the modified propylene homopolymer described above and an unmodified propylene homopolymer. In this case, the mixture has preferably an MFR of 60 g/min or more, more preferably 100 g/min or more and further more preferably 100 to 1,000 g/min.
The unsaturated carboxylic acid or anhydride thereof described above includes acrylic acid, methacrylic acid, maleic acid, nadic acid, fumaric acid, itaconic acid, maleic anhydride, nadic anhydride and itaconic anhydride, and maleic anhydride is preferred from a viewpoint of a glass fiber-reinforcing effect.
To be specific, magnesium hydroxide, calcium hydroxide and magnesium oxide are given as examples of the simple substances, hydroxides and oxides of alkaline earth metals of (A2) described above constituting (A) the long fiber-reinforced polypropylene homopolymer pellet of the present invention. They can be used alone or in combination of two or more kinds thereof. Magnesium hydroxide is preferably used from a viewpoint of an effect for improving the mechanical strength and the impact resistance.
A continuous glass fiber bundle is used as a raw material for the glass long fiber of (A3) described above having a length of 2 to 50 mm constituting (A) the long fiber-reinforced polypropylene homopolymer pellet of the present invention, and this is commercially available as glass roving. Usually, it has an average fiber diameter of 4 to 30 xcexcm, a filament concentrating number of 400 to 10,000 filaments and a tex yarn number count of 300 to 20,000 g/km, and it has preferably an average fiber diameter of 9 to 23 xcexcm and a concentrating number of 1,000 to 6,000 filaments. From a viewpoint of a reinforcing effect, it is preferably subjected on a surface thereof to silane coupling agent treatment for the sake of providing the resin with a surface adhesive property.
The blending proportions of (A1) to (A3) are (A1) 20 to 64.9% by weight, (A2) 0.1 to 5% by weight and (A3) 35 to 75% by weight based on (A), that is, the pellet.
Any of processes publicly known as a pultruding process can be employed as a production process for the long fiber-reinforced propylene homopolymer pellet of (A). Usually, employed is a process in which a molten resin comprising (A1) and (A2) is fed from an extruding machine into an impregnating dice provided at a tip of the extruding machine and, the continuous glass fiber bundle which is a raw material of (A3) is passed therethrough to impregnate the above glass fiber bundle with the molten resin and in which it is then pultruded through a nozzle and pelletized into a length of 2 to 50 mm.
Capable of being taken as a method for feeding (A1) and (A2) are:
1) a method in which the modified propylene homopolymer and the alkaline earth metal compound (at least one selected from the group consisting of simple substances, hydroxides and oxides) are dry-blended and put into a hopper of an extruding machine to feed them,
2) a method in which the modified propylene homopolymer, the unmodified propylene homopolymer and the alkaline earth metal compound (at least one selected from the group consisting of simple substances, hydroxides and oxides) are dry-blended and put into a hopper of an extruding machine to feed them,
3) a method in which the propylene homopolymer, the unsaturated carboxylic acid or anhydride thereof, the organic peroxide and the alkaline earth metal compound (at least one selected from the group consisting of simple substances, hydroxides and oxides) are dry-blended and put into a hopper of an extruding machine to feed them while carrying out modification at the same time, and
4) a method in which an extruding machine having at least two raw material-feeding ports is used and while putting thereinto a dry-blended mixture of the propylene homopolymer, the unsaturated carboxylic acid or anhydride thereof and the organic peroxide from the first feeding port to carry out modification, the alkaline earth metal compound (at least one selected from the group consisting of simple substances, hydroxides and oxides) is put thereinto from the second feeding port to feed them. The methods 1), 2) and 4) are preferred from a viewpoint of an effect for improving the mechanical strength and the impact resistance.
Any-of publicly known methods can be employed as the impregnating method as long as they are methods in which a good impregnating property is achieved. Capable of being employed is any of a method in which a glass fiber bundle is brought into contact with a surface of a spreader and passed thereon while applying tension to thereby impregnate it with a molten resin (Japanese Patent Publication No. 37694/1988) and a method in which a glass fiber bundle is passed between a pair of opening pins provided in an impregnating dice in a non-contact state to thereby impregnate it with a molten resin (International Publication WO97/19805). The latter is a preferred method from a viewpoint of providing less problem on fluffing of a glass fiber bundle after passing nozzle at a high speed.
Used as the diluent of (B) is a crystalline propylene base block copolymer resin of propylene with other xcex1-olefins such as ethylene, 1-butene and 1-pentene having a propylene content of 70% by weight or more. The form of the propylene base block copolymer resin may be pelletal, granular, flaky or powdery and shall not specifically be restricted, and the pelletal one is preferably used. The propylene base block copolymer resin has an MFR of 50 g/min or less, preferably 35 g/min or less and more preferably 5 to 35 g/min from a viewpoint of an effect for improving a mechanical strength and an impact resistance.
Similarly from a viewpoint of an effect for improving a mechanical strength and an impact resistance, preferably used as (B) is a high rigid propylene-ethylene block copolymer resin comprising a propylene homopolymer part having an isotactic pentad rate of 0.96 or more and a weight average molecular weight/number average molecular weight (Mw/Mn; so-called Q value) of 6 or less, and a propylene-ethylene block copolymer part. In this case, the isotactic pentad rate shows an isotactic rate in terms of a pentad unit in a molecular chain and can be determined based on Macromolecules 8, 687 (1975) using 13C-NMR. Further the respective average molecular weights of Mw and Mn can be determined by means of GPC (gel permeation chromatography).
Similarly from a viewpoint of an effect for improving a mechanical strength and an impact resistance, preferably used as (B) is a propylene base block copolymer resin containing 0.0001 to 1% by weight of a nucleating agent based on the propylene base block copolymer resin. In this case, capable of being given as examples of the nucleating agent contained in the propylene base block copolymer resin are talc, succinic acid, lithium benzoate, sodium benzoate, aluminum hydroxy-bis(4-t-butylbenzoate), 1xe2x80xa23,2xe2x80xa24-dibenzylidenesorbitol, 1xe2x80xa23,2xe2x80xa24-bis(p-methylbenzylidene)sorbitol, 1xe2x80xa23,2xe2x80xa24-bis(p-ethylbenzylidene)sorbitol, 1xe2x80xa23,2xe2x80xa24-bis(2xe2x80x2,4xe2x80x2-dimethylbenzylidene)sorbitol, 1xe2x80xa23,2xe2x80xa24-bis(3xe2x80x2,4xe2x80x2-dimethylbenzylidene)sorbitol, 1xe2x80xa23-p-chloro-benzylidene-2xe2x80xa24-p-methylbenzylidenesorbitol, sodium-bis(4-t-butylphenyl)phosphate, sodium-2,2xe2x80x2-methylene-bis(4,6-di-t-butylphenyl)phosphate, a mixture (1:1:1 weight ratio)) comprising three components of aluminum dihydroxy-2,2xe2x80x2-methylene-bis(4,6-di-t-butylphenyl)phosphate, aluminum hydroxy-bis[2,2xe2x80x2-methylene-bis(4,6-di-t-butylphenyl)-phosphate] and lithium stearate, poly-3-methyl-1-butene, polyvinyl-cyclohexane, polyallyltrimethyl-silane and N,Nxe2x80x2-dicyclohexyl-2,6-naphthalenedicarboxyamide.
(A) can be blended with (B) by a dry blending system. It is rather preferred that they are fed directly into a molding machine such as an injection-molding machine after dry-blending without passing through an extruding machine in order to maintain a length of the fibers contained in the composition and obtain a higher effect for improving a mechanical strength and an impact resistance. The blending proportion thereof is determined depending on a glass fiber content in the long fiber-reinforced propylene homopolymer pellet of (A) and a glass fiber content required to the finished molded article, and it is (A) 40 to 85% by weight and (B) 15 to 60% by weight from a viewpoint of an effect for improving the mechanical strength and the impact resistance.
In addition to those described above, an antioxidant, a light stabilizer, a UV absorber and an antistatic agent can be added, if necessary, to the composition of the present invention.
Publicly known molding methods such as an injection-molding method, an extrusion-molding method, a blow-molding method, a compression-molding method and an injection compression-molding method can be applied to a production method for a molding article obtained from the long fiber-reinforced polypropylene resin composition without any restrictions. In particular, an injection-molding method, a compression-molding method and an injection compression-molding method are preferred. The resulting molded article can widely be used in various uses from small-sized to large-sized ones. In particular, it can be used in uses for medium-sized to large-sized molded articles for automobiles.